1. Technical Field
The present invention relates to a two-component developer used in an image forming apparatus of an electrophotographic system represented by copying machines and printers.
2. Description of Related Arts
In recent years, copying machines and printers of electrophotographic system have been subjected to attempts to increase a printing speed, and among developers used in those apparatuses, two-component developers that are advantageous in high-speed development have been in the mainstream. A two-component developer is composed of a magnetic powder called a carrier, and a toner. It is believed that a two-component developer is advantageous in high-speed development since a desired amount of electric charge can be rapidly given to a toner by mechanically stirring the toner and a carrier. Functions required for a carrier include frictional chargeability appropriate to a toner, fluidity, developability, high durability capable of withstanding long-term use, and the like. In order to enhance these functions, a carrier of a type called resin-coated carrier, which is formed by coating a surface of core material particles that are formed of a ferromagnetic metal or an oxide thereof with a resin, has been widely used.
An example of the resin used for the resin-coated carrier (hereinafter, also referred to as resin for coating) is a resin formed by polymerizing a methacrylic acid cycloalkyl ester which is an alicyclic methacrylic acid ester. Although a carrier formed by using the resin has excellent frictional chargeability and excellent moisture resistance, it has problems such that after long-term endurance, the resin layer (hereinafter, also referred to as coating resin layer) may be detached from the surface of the core material particles due to friction, and contamination caused by the attachment or embedment of an external additive to the toner is likely to occur to induce decrease in amount of electric charge. As a measure against such friction of the resin for coating, for example, it has been suggested in Japanese Patent No. 3691085 that friction properties may be significantly improved by using a resin produced by copolymerizing a chain methacrylic acid ester with an alicyclic methacrylic acid ester.